3. Now the noise will be multi-colored, that's usually not useful to us, we only want a greyish color. To fix this go to Filter > Color > Greyscale. Here I usually choose Average but you can choose anything, but make sure there is not too much white noise that doesn't help.

4. Now to make the noise look like rain, go to Filter > Visual Effect > Motion Blur... Usually Level 2 is fine. Now usually the rain is falling downwards so adjust the direction so the 2 colored circles are vertical. But you are free to put at any angle.

5. Now you have the right effect but you need to change the blend mode of the layer so the black background becomes invisible. To do this, click the layer manager tool, which should also be accessible by clicking W on your keyboard. If done correctly, you should now see a blend mode at the bottom right of the screen. Usually this is set to Normal, but you should set it to Screen. After setting it to screen you should now see the image below and have rain falling in the background. If you feel the rain effect is too strong, there is an option above the Blend mode called Opacity, simply adjust this to under 100% and you should be able to get the effect you want.